Japanese Patent Publication No. 6-291368 discloses a semiconductor light emitting device designed to radiate a light effectively. The device includes a crystalline substrate made of sapphire on which two semiconductor layers of opposite conductive types are developed. A pair of electrodes is provided to apply a voltage across an interface between the two semiconductor layers for generating a light from around the interface. An exposed or outer one of the two semiconductor layers is finished to have an irregular surface with an array of minute concavities. With the formation of the irregular surface, it is intended to reduce multiple reflections within the outer semiconductor layer for giving off the light in a large extent through the irregular surface. However, due to a structural restriction that the outer semiconductor layer is covered by the electrode, the light radiation surface has to be correspondingly reduced and therefore the light radiation surface is restricted. In addition, the crystalline substrate essential for developing thereon the semiconductor layers is not utilized as giving a light radiation surface with the irregular surface, although the crystalline substrate could have a wider radiation surface than the outer semiconductor layer covered with the electrode.